1. Field of the Invention
This invention relates to an exhaust system, an exhaust process, and a vacuum processing apparatus and a vacuum processing method which have the exhaust system. More particularly, it relates to an exhaust system, an exhaust process, and a vacuum processing apparatus and a vacuum processing method which have the exhaust system. The exhaust system is suitable for use in a vacuum processing apparatus including a deposited-film-forming apparatus that can form crystalline or non-single crystal functional deposited films useful in producing semiconductor devices, such as electrophotographic photosensitive member devices, image-inputting line sensors, image pick-up devices and photovoltaic devices, a sputtering apparatus that can preferably form insulating films and metallic wiring for semiconductor devices and optical devices, and an etching apparatus for semiconductor devices.
2. Related Background Art
Various plasma processing apparatuses are used for a variety of purposes. For example, oxide films or nitride films are formed by plasma CVD using a plasma CVD system, and semiconductor films as typified by amorphous silicon films are also formed. Also, metal films used as metallic wiring films are formed by sputtering using a sputtering apparatus, or processing targets are etched using an etching apparatus which enables fine processing. Development of such techniques is in progress. In particular, plasma processing making use of high-frequency power or microwave power has a high stability in discharging and is used because of its various advantages, e.g., it can be used in forming not only semiconductor films but also insulating materials such as oxide films and nitride films.
Now, in vacuum processing, in recent years there has been a strong demand for an improvement in film quality of films formed and process capability therefor, and various measures are being studied. In particular, from the viewpoint of improving film quality, increasing film quality unformity and controlling film thickness, making the degree of vacuum higher in the discharge space has been studied. For example, deposited-film-forming apparatuses are known to attain a high degree of vacuum by using a diffusion pump in combination with a rotary pump or mechanical booster pump, the former being a pump for evacuating the inside of a processing space and the latter being an auxiliary pump for assisting the evacuation made by the diffusion pump. The rotary pump or mechanical booster pump is used for roughing. In such an instance, the degree of vacuum achieved in the discharge space can be from about several hundred Pa to about 20 Pa. At present, a high degree of vacuum from about 10 mPa to 15 Pa can also be achieved by optimizing the form of evacuation. In such deposited-film-forming apparatuses, deposited films with less contamination and improved properties can be obtained by making the degree of vacuum in the discharge space higher.
In order to decrease production cost, it is important to improve the rate of deposition of functional films (i.e., rate of vacuum processing). Making the rate of deposition (rate of vacuum processing) higher brings about a higher throughput of the deposited-film-forming apparatus (vacuum processing apparatus). As a result, the cost necessary for plant investment can be reduced, and the processing cost for individual products can be reduced. Accordingly, in order to make the rate of processing higher while making it possible to improve film quality, increase film quality uniformity and control film thickness with ease, it is necessary to evacuate the inside of a processing chamber of the vacuum processing apparatus at a high rate and to a high vacuum by means of a vacuum pump with a large exhaust capacity, while feeding material gases at high flow rates to the vacuum processing apparatus.
Meanwhile, when material gases are exhausted at a high rate by means of a vacuum pump having a large exhaust capacity, it is preferable to use the diffusion pump. The diffusion pump can readily attain a large exhaust capacity, and the pump itself is inexpensive. When the diffusion pump is used in combination with the mechanical booster pump or rotary pump, the degree of vacuum attained can be 10 mPa to 15 Pa as stated above, and hence the above intended performance can be achieved sufficiently.
However, when such material gases fed at high flow rates are exhausted by the diffusion pump, diffusion pump oil vaporized from the diffusion pump flows to the side of the auxiliary pump mechanical booster pump or rotary pump together with the material gases to be exhausted. This results in an abrupt decrease in the quantity of the diffusion pump oil in the diffusion pump. The diffusion pump oil is expensive. The consumption of diffusion pump oil in a large quantity causes high production cost. Also, in order to supplement the diffusion pump oil, it is necessary to provide the steps of cooling the diffusion pump, thereafter restoring the internal vacuum state to the atmospheric pressure and then supplementing the diffusion pump oil. Frequent repetition of such steps results in a low operating efficiency of the system. Also, it is necessary to provide more maintenance to the diffusion pump. In addition, the oil flowed out of the diffusion pump to the auxiliary pump side stands in the auxiliary pump rotary pump. Such oil in the rotary pump may increase with long-term continuous use and eventually cause trouble. Even if it does not lead to trouble, it has ill effects such as lowering exhaustion rate and conspicuous suspension of oils when oils different in properties are present. Moreover, since the diffusion pump oil which is not the oil for the rotary pump enters the rotary pump, it may cause wear of the rotary pump at its sliding faces and other problems which shorten the rotary pump lifetime. Of course, such problems are applicable similarly to a vacuum processing apparatus such as a deposited-film-forming apparatus, a sputtering apparatus and an etching apparatus.
An object of the present invention is to provide an exhaust system, an exhaust process, a vacuum processing apparatus and a vacuum processing method which can solve the above problem.
Another object of the present invention is to provide an exhaust system, an exhaust process, a vacuum processing apparatus and a vacuum processing method which, even when material gases fed at high flow rates are exhausted, do not result in diffusion pump oil flowing to the auxiliary pump side, thereby abruptly decreasing the amount of diffusion pump oil and causing such oil to stand in the auxiliary pump, which are durable to repeated use, which can maintain evacuation performance over a long period of time and which can achieve maintenance cost reduction.
Still another object of the present invention is to provide an exhaust system, an exhaust process, a vacuum processing apparatus and a vacuum processing method which enable easy and inexpensive control of vacuum processing, e.g., to improve film quality, to increase film quality uniformity and to control film thickness.
A further object of the present invention is to provide an exhaust system, an exhaust process, a vacuum processing apparatus and a vacuum processing method which make it easy to keep any contamination of processing targets to a minimum in the course of the manufacturing process.
A still further object of the present invention is to provide an exhaust system, an exhaust process, a vacuum processing apparatus and a vacuum processing method which enable short-time production and cost reduction and promise good reproducibility of vacuum processing.
To achieve the above objects, the present invention provides an exhaust system comprising:
a first exhaust means;
a second exhaust means for exhausting an exhaust gas of the first exhaust means;
an exhaust line connecting the first exhaust means and the second exhaust means; and
a cooling means for cooling the exhaust line, provided along the exhaust path.
The present invention also provides an exhaust process comprising the steps of:
exhausting an exhaust gas of a first exhaust means through a second exhaust means which connects the first exhaust means through an exhaust line;
liquefying in the exhaust line by a cooling means the exhaust gas flowing from the first exhaust means through the exhaust line; and
exhausting by the second exhaust means the exhaust gas having passed through the step of liquefying the exhaust gas.
The present invention still also provides a vacuum processing apparatus comprising a reactor and a vacuum pump connected to the reactor to draw up a gas held in the reactor, the vacuum pump comprising a diffusion pump and an auxiliary pump, the apparatus further comprising:
an exhaust line provided between the diffusion pump and the auxiliary pump; and
a cooling unit provided in the exhaust line, for cooling the gas to liquefy or condense an oil smoke comprised of a diffusion pump oil contained in the gas, to cause the resultant oil to deposit in the exhaust line.
The present invention further provides a vacuum processing method for forming a deposited film by a system comprising a reactor and a vacuum pump connected to the reactor to draw up a gas held in the reactor; the vacuum pump comprising at least a diffusion pump and an auxiliary pump; wherein
the diffusion pump and the auxiliary pump are connected through an exhaust line and a cooling unit is provided in the exhaust line, where the gas is cooled by the cooling unit to liquefy or condense an oil smoke comprised of a diffusion pump oil contained in the gas, to cause the resultant oil to deposit in the exhaust line.